1. Field of the Invention
The present invention relates to an imaging apparatus, particularly relates to the imaging apparatus having function of automatic focus.
2. Description of the Related Art
Generally, the imaging apparatus such as a digital still camera has automatic focus (hereinafter referred to as “AF”) having function adjusting automatically focus. Hill climbing control described in Japanese Patent Application Publication No. 39-5265 is widely used as the function. The hill climbing control is that an integral value of a high frequency component or brightness difference in adjacent pixels is calculated from image data obtained by an imaging element such as a CCD and the integral value is changed into an AF evaluation value showing a degree of the focus.
In the case of a focused state, because an edge portion of a subject is clear, the AF evaluation value becomes large, and in the case of an unfocused state, the AF evaluation value becomes small. An AF apparatus takes the AF evaluation value in order while the AF apparatus moves a lens from an infinite distance to a close distance, and the AF apparatus stops the lens at a focal position where the AF evaluation value becomes a maximum.
In the apparatus imaging a still image such as the digital still camera, generally the strict focus required compared with the apparatus imaging a dynamic picture image such as a video camera, so that focusing operation is performed for every imaging operation or the focusing operation is always repeated.
However, when the hill climbing control AF is performed for every imaging operation, there is a problem that release time lag between imaging start request manipulation of an operator and actual imaging performance occurs. When the focusing operation is performed for every imaging operation or the focusing operation is performed repeatedly, because the lens is moved by a motor during the focusing operation, electric current is increased and a battery life is shortened.